In general, a wireless LAN system is formed by wireless mobile terminals and an access point device. Note that the wireless mobile terminals are wireless terminal devices which make data communications with each other via a wireless transmission path and wired LAN. The access point device is a wireless control device which makes wireless communications with a plurality of wireless mobile terminals within a service area, and has a bridge or router function that connects a wireless section and wired LAN.
IEEE 802.11 as the standard of a wireless LAN specifies a wireless access protocol between a wireless access station and terminal. The wireless access protocol specifies DCF as a contention-based random access function based on CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). The DCF is an abbreviation for Distributed Coordination Function. The DCF further specifies CFP (Point Coordination Function) as an optional function. This CFP is a function of periodically setting a CFP (Contention Free Period) on a wireless transmission path used by a wireless access station to communicate with a terminal, and making contention free access by polling during the CFP duration.
The aforementioned IEEE 802.11 standard specifies various parameters of the DCF and CFP. However, in this standard, the control of the DCF and CFP depends on an implemented product, and no detailed contents are specified. Under such background, some implementation methods have been proposed.
For example, Japanese Patent Laid-Open No. 2002-185462 proposes a method of switching selection of a communication mode depending on application purposes. More specifically, when data to be exchanged places an importance on realtimeness, the CFP as a central control type communication mode is selected. When an importance is placed on reliability, the DCF as a distributed autonomous type communication mode is selected.
As another implementation method, for example, Japanese Patent Laid-Open No. 2003-198564 (US2003125087A1) proposes a method of switching a communication mode depending on the situation. With this reference, an AP (Access Point) detects the average data size of data frames exchanged with an STA (Station). When a state in which the average data size exceeds a predetermined value continues for a predetermined period of time, the communication mode is switched from the DCF to the CFP. Alternatively, when a state in which the ratio of transmission data stored in the AP itself exceeds a predetermined value continues for a predetermined period of time, the communication mode is switched from the DCF to the CFP.
Furthermore, for example, Japanese Patent Laid-Open No. 2004-40336 (US2004038684A1) proposes still another method of switching a communication mode depending on the situation. With this reference, an AP performs transmission/reception based on the DCF method initially. When a data size stored in a buffer exceeds a predetermined value, the communication mode is switched to the CFP. When no data is stored in the buffer, the communication mode is switched to the DCF.
On the other hand, as a recent trend, a concept called QoS (Quality of Service) is introduced into these data communications as wireless transmission. In order to assure the priority order and bandwidth depending on the contents and purpose of data, task group TGe of IEEE 802.11 makes examination. In the following description, task group TGe IEEE 802.11 will be referred to as IEEE 802.11e.
In IEEE 802.11e (see IEEE 802.11e/D8.0 February 2004), a connection transmission path of data to be wirelessly transmitted is called traffic stream TS. A data type called access category AC according to the data contents is specified for each traffic stream TS. Furthermore, as a distributed control method which specifies the priority order for respective access categories AC, and implements access control according to the priority order, an EDCA (Enhanced Distributed Channel Access) access control method is specified. Moreover, as a central control method that implements access control according to the priority order, an HCCA (Hybrid coordination function Controlled Channel Access) access control method is specified.
By contrast, in the prior art described in Japanese Patent Laid-Open No. 2002-185462, one of the CFP and DCF is selected with reference to the realtimeness and reliability of data to be exchanged, as described above. That is, the communication mode is selected irrespective of the connection situation of wireless client terminals (wireless terminal devices) within a wireless service area in which they are connected and accommodated. Such implementation method is not preferable in terms of QoS control in the service area which includes different access control methods together.
In the prior art described in Japanese Patent Laid-Open No. 2003-198564 (US2003125087A1), the communication mode is switched from the DCF to the CFP when a state in which the average data size of data frames to be exchanged exceeds a predetermined value continues for a predetermined period of time. Alternatively, when a state in which the ratio of transmission data stored in a wireless control device itself exceeds a predetermined value continues for a predetermined period of time, the communication mode is switched from the DCF to the CFP. That is, the prior art is limited to data transmission control from the wireless control device to wireless client terminals. For this reason, this technique cannot be applied to QoS control associated with the uplink in a direction from the wireless client terminal to the wireless control device.
Furthermore, the prior art described in Japanese Patent Laid-Open No. 2004-40336 (US2004038684A1) is also intended for data transmission control from the wireless control device to the wireless client terminals, and determines the traffic state based on the remaining size of the data buffer in the wireless control device. For this reason, this technique cannot be applied to QoS control associated with the uplink in a direction from the wireless client terminal to the wireless control device. That is, the techniques described in Japanese Patent Laid-Open Nos. 2003-198564 (US2003125087A1) and 2004-40336 (US2004038684A1) are QoS control on the initiative of the wireless control device.
As described above, the aforementioned prior arts merely describe QoS control associated with data transmission in a downstream direction from a coordinator that controls the CFP method to wireless client terminals. As for QoS control associated with data transmission in an upstream direction from the wireless client terminal to the wireless control device, no solution is described.
In any case, since the special QoS control in the initiative of the wireless control device is provided, the wireless control device must comprise an expansive or additional QoS control function (within the service area), resulting in an increase in cost of the device itself.